The present invention relates to an amplitude-controlled electronic device, such as an oscillator device, intended to generate an alternating output signal of substantially constant amplitude in accordance with the preamble of claim 1.
A solution for controlling of the amplitude of an alternating output signal generated by an electronic device, such as an oscillator circuit, typically consists in providing the electronic device with an amplitude control loop. This amplitude control loop typically includes a measuring branch intended to generate a measuring voltage representative of the amplitude of the output signal, such measuring voltage being compared to a reference value in order to generate a control signal, or slaving signal, which is applied to the electronic device for the purpose of slaving the output signal to a determined value.
A drawback of this solution lies in the fact that the measuring branch allowing the measuring voltage representative of the output signal amplitude to be generated is commonly sensitive to temperature variations and is sensitive to variations in the manufacturing process. This sensitivity has direct repercussions on the control signal so that a constant output signal amplitude cannot be guaranteed with such a solution.
A main object of the present invention is thus to propose an electronic device wherein the amplitude control of the output signal is in particular substantially independent of variations in temperature and manufacturing processes.
Document U.S. Pat. No. 3,828,270 already describes an amplitude-controlled electronic device fulfilling the above-mentioned main object. This document describes a device for generating an alternating output signal and comprising a measuring branch for generating a measuring voltage representative of the amplitude of the alternating output signal, a reference branch for generating a reference voltage and comparator means for comparing the measuring and reference voltages and for generating a control signal of the amplitude of the output signal. The measuring and reference branches are matched so as to exhibit similar sensitivity to temperature and manufacturing process variations. The device however requires an additional source for generating the reference voltage as well as attenuators pour setting the value of this reference voltage, the characteristics of these attenuators being adjusted by hand.
Another object of the present invention is thus to propose a solution which is more simple in design that prior art solutions and which is in particular suited for low consumption applications.
The present invention therefore concerns an amplitude-controlled electronic device whose features are listed in independent claim 1.
Advantageous embodiments form the subject of the dependent claims.
According to the invention, the reference voltage is thus generated at the output of a reference branch matched with the measuring branch which generates the measuring voltage representative of the amplitude of the electronic device output signal, such reference voltage being in particular obtained by switching a voltage reference at the input of the measuring branch. The result of matching the measuring and reference branches is that the sensitivity to temperature and manufacturing process variations of these voltages are substantially equal so that the control signal generated in response to the comparison of such voltages is substantially independent of these variations.
The switching frequency of the voltage reference may in particular be selected to be lower that the frequency of the alternating signal generated at the output of the electronic device, thereby lowering the consumption of the control system.
Preferably, the switching frequency of the voltage reference is derived from the frequency of the alternating output signal generated by the electronic device. Accordingly, it is not necessary to use an additional source for generating the reference voltage.